Gloss-coated papers suitable for electrophotographic printing are in demand due to their superior image quality and toner adhesion properties as compared to uncoated paper grades. The surface of a gloss-coated sheet is very smooth as a result of calendering operation. The high smoothness is attributed to many advantageous imaging performances, however, it also presents challenges for the runnability of gloss coated paper in sheet-fed digital equipment such as color copiers and laser and color laser printers. Coated papers are also more susceptible to blistering due to high fusing temperatures in colour copiers and even some high-speed black and white copiers. The following coated paper designs have been proposed in the literature.
WO 00/40424 discloses a multi-layer coated copy paper, which has a thermal insulating layer, between the base paper layer and the outer topcoat layer. The thermal insulating layer contains from 10% to 70% calcium carbonate, from 90% to 30% fully or partially calcined clay and from 0% to 30% satin white with a binder.
U.S. Pat. No. 4,301,210 discloses a high quality cast coated paper with an aqueous undercoat layer and an aqueous overcoat layer. The undercoat layer was applied using a blade coating, The overcoat layer was applied using a cast coating method. The overcoat layer contains a polymer latex with a glass transition temperature of 38 degree Celsius or higher. The overcoat was dried at temperature below the glass transition temperature of the polymer latex. A glossy finish was obtained by subjecting the overcoat surface to mirror finish treatment at a temperature higher than the glass transition temperature of the polymer latex.
U.S. Pat. No. 4,317,849 discloses a high-gloss coated paper with an aqueous coating comprising a synthetic polymer latex (A) having a glass transition temperature of at least 38 degree Celsius and a synthetic polymer latex (B) having a glass transition temperature of 5 to 25 degree Celsius. The weight ratio of A to B is from 1/0.1 to 1/1. The coated surface was subjected to hot roll calendering at temperatures higher than the glass transition temperature of polymer latex A.
U.S. Pat. No. 5,360,657 discloses a process to produce coated printing paper by first applying a pigment coating layer and applying a thermal plastic latex with a second order transition temperature of at least 80 degrees Celsius and an average particle size of smaller than 100 nm. High gloss is obtained by adding lubricants to the surface layer and calendering at 10 to 30 degree Celsius.
EP 1 045 068 A2 discloses a coated paper product having high gloss and brightness. The paper substrate is coated on at least one side with an aqueous coating formulation comprising an effective amount (14–35% by weight) of a plastic pigment and finished in a supercalender device.
U.S. Pat. No. 5,965,315 discloses a transfer sheet for electrophotography, which comprises a substrate coated with a porous resin-containing layer. The coated layer has a surface average pore diameter of 0.5 to 50 micrometer. The transfer sheet is said to be capable of eliminating mottles and dots and minimum gloss contrast between the blank portion and the image portion.
U.S. Pat. No. 5,254,403 discloses a recording sheet which comprises a substrate and an image receiving layer comprising a mixture of (a) a polymer capable of forming a latex, (b) a polysaccharide; and (c) a polymer containing oxyalkylene monomers. The recording sheets are suitable to use in both inkjet and electrophotographic imaging processes.
U.S. Pat. No. 5,952,082 discloses a coated paper particularly suitable for electrophotographic copying. The coated paper has a given basis weight with proportionally less coating and proportionally more fiber than conventional coated paper made for electrophotographic processes. The coated sheet is calendered to achieve a TAPPI 75 degree gloss value of about 45. The coated paper is said to have good fusing of dried toner on the paper at marginally lower temperatures. The typical properties are as follows: 45 gloss; 87 brightness, 91.5 opacity (for 70 # paper); and 2.1–2.3 Parker Print Smoothness.
U.S. Pat. No. 4,198,471 discloses a coated printing paper using a pigment system comprising a combination of a thermoplastic polymer and a thermosetting polymer. The amount of thermoset is preferably at least about 25% by weight of the pigment solids to provide improved ink receptivity and paper gloss. The amount of the thermoset is preferable below 75% by weight of the pigment solids so that the finished printing paper has a Gardner 75 degree gloss of at least about 40, using a calendering pressure of less than 500 PLI.
U.S. Pat. No. 5,846,637 discloses a coated xerographic photographic paper comprised of (1) a cellulosic substance; (2) a first antistatic coating layer in contact with one surface of the substrate: (3) a second toner receiving coating on top of the antistatic layer; and (4) a third traction controlling coating in contact with the back side of the substrate.
U.S. Pat. No. 4,778,711 discloses a coated electrophotographic image transfer paper that reduces blistering during fixing. The coated electrophotographic image transfer paper has a center-line-average surface roughness of not more that 2.0 micrometer and air permeability of less than 4,000 seconds.
None of the coating designs in the prior arts overcomes the shortcomings of blistering, feeding jams in high-speed copiers. The objective of the present invention is to address these performance shortcomings of coated electrophotographic paper.